Semi-continuous casting method utilizing a thermoinsulating sheet material

ABSTRACT

A method for the semi continuous casting of metal in a mould having a vertical wall structure and a dummy which is initially disposed within the lower part of that wall structure, said dummy being lowered progressively from the wall structure as metal in the mould solidifies and casting proceeds, in which before the metal is poured into the mould a strip of heat resistant and thermally insulating sheet material, preferably woven fiber glass material, is laid on part of the inside of the wall structure immediately above the upper surface of the dummy and preferably extending a short distance round the corner onto the top of the dummy, so that it covers at least part of the side of the lower end of the cast metal as it emerges from the mould thus reducing the differential shrinkage between the metal first solidified on the dummy and that immediately following causing a reduction in the degree of upward bowing of the edges of the bottom surface of the billet. The sheet material can extend continuously up the wall structure to the top of the mould and then prevents blebs forming on the sides of the cast product.

llnited States Patent 119 Clegg SEW-CUNTINUOUS CASTING METHOD UTlLIZlNG A THERMOINSULATING SHEET MATERIAL [75] Inventor: Robert Stanley Clegg, Stirling, Scotland [73] Assignee: The British Aluminum Company Limited, London, England [22] Filed: Mar. 4, 1971 21 Appl. No.1 120,947

[30] Foreign Application Priority Data Mar. 12, 1970 Great Britain ..l1,978/70 52 us. 01 ..164/82, 164/274 51 1111.01. ..B22d 11/10 [58] Field of Search ..l64/89, 72, 73, 74,

[ 51 Apr. 10, 1973 5/1968 Gardner ..164/73 l/l959 Patterson ..164/362 ABSTRACT A method for the semi continuous casting of metal in a mould having a vertical wall structure and a dummy which is initially disposed within the lower part of that wall structure, said'dummy being lowered progressively from the wall structure as metal in the mould solidities and casting proceeds, in which before the metal is poured into the mould a strip of heat resistant and thermally insulating sheet material, preferably woven fiber glass material, is laid on part of the inside of the wall structure immediately above the upper surface of the dummy and preferably extending a short distance round the corner onto the top of the dummy, so that it covers at least part of the side of the lower end of the cast metal as it emerges from the mould thus reducing the differential shrinkage between the metal first solidified on the dummy and that immediately following causing a reduction in the degree of upward bowing of the edges of the bottom surface of the billet. The sheet material can extend continuously up the wall structure to the top of the mould and then prevents blebs forming on the sides of the cast product.

7 Claims, 4 Drawing Figures PATENTEDAPRI 0l973 SHKEI 1 OF 2 PMFNTEDHR 1 01m SHEET 2 BF 2 SEMI-CONTINUOUS CASTING METHOD UTILIZING A THERMOINSULATING SHEET MATERIAL BACKGROUND OF THE INVENTION This invention relates to the casting of metal, and is particularly concerned with the semi-continuous casting of metals such as aluminum and aluminum alloys.

In the continuous casting of metal (particularly aluminium alloys) molten metal is poured into a mould, usually of generally rectangular cross-section, the bottom of which is formed by a starting block or dummy. The metal poured into the mould solidifies on the dummy to a depth of some 1 to 2 inches, and as casting continues, the dummy is lowered from the mould so that an elongated solid billet is continuously formed by molten metal within the mould solidifying on top of the previously solidified metal of the billet leaving the bot tom of the mould.

In such a casting operation, when the dummy leaves the mould and the lower end of the billet emerges from the mould, the metal of the billet which follows contracts more than the solid metal immediately on the dummy. This differential shrinkage results in the bottom surface of the billet bowing upwards away from the dummy at the edges, with the result that the faces of the billet which are still in the mould, are pulled away from contact with the mould and lead to local necking. Such loss of contact between the necked area of the billet and the mould wall and the consequent reduction of cooling, may result in local remelting of the necked Again during the continuation of the casting process I as the molten metal solidifies against the walls of the mould and the billet moves downwards through the mould, shrinkage of the billet causes the solidified surface of the billet to lose contact with the walls of the mould with a resultant marked reduction in heat transfer from the surface of the billet. Again, the solidified surface can then remelt locally allowing molten metal from within the billet to form protruberances or blebs on the surface of the cast billet. Such blebs also detract from the qualities of a cast billet which is to be rolled down to a slab or to sheet stock subsequent to casting, and in particular promote edge cracking during the rolling operation.

It is an object of the present invention to provide a method of semi-continuous casting of metal which alleviates these problems.

SUMMARY OF INVENTION Accordingly, the present invention provides a method for the semi-continuous casting of metal in a mould having a wall structure and a starting block or dummy initially disposed within the lower part of that wall structure, said dummy being lowered progressively from the wall structure as casting proceeds, comprising laying, before metal is poured into the mould, a strip of heat resistant material around at least part of the peripheral corner formed betweenthe dummy and the inside of said wall structure, said strip extending onto the upper surface of the dummy and extending at least a short distance up the wall structure of the mould.

In a preferred arrangement of the invention, the mould is of generally rectangular cross-section, and said strip of material is laid in said corner along one or more sides of the mould.

Preferably the heat resistant material is fiber glass cloth material.

Preferably the fiber glass cloth material is a woven fabric.

In a development of the above preferred arrangement, the strip of material as laid along at least one side of the rectangular cross-section may be arranged to extend up the full height of the respective side wall of the mould in a continuous sheet to lie between metal cast in the mould and that side wall, means being provided to feed said sheet to so lie continuously with the lowering of said dummy.

BRIEF DESCRIPTION OF DRAWINGS In order to promote a fuller understanding of the above, and other, aspects of the present invention, two embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a mould arrangement for the continuous casting of metal, in an initial state ready for the commencement of casting,

FIG. 2 is a schematic cut away perspective view of the mould of FIG. 1 arranged in accordance with one embodiment of the invention,

FIG. 3 is a similar view to that of FIG. 2 at a later stage in the casting of a billet arranged in accordance with a second embodiment of the invention, and

FIG. 4 is a series of side view of the lower end of a lata east- FIG. 1 shows a cross-sectional view o f the arrangement of a mould and starting block or dummy for the continuous casting of metal.

DESCRIPTION OF PREFERRED EMBODIMENTS The arrangement includes a mould l of generally rectangular cross-section and a dummy 2 corresponding in cross-section to the mould l and arranged initially in the bottom of the mould 1 to form the bottom wall thereof. The dummy 2 is provided with means (not shown) whereby the dummy may be lowered progressively from the mould 1 after commencement of and during the continued casting of metal in the mould 1.

The wall strength of the mould l is surrounded by a water-jacket 3 arranged to collect water from a series of water spray jets 4 which are arranged around the mould I so that in operation, jets of water impinge on the outer surfaces of the mould 1 to cool it, and the water runs down into the water-jacket 3 to collect therein. The water-jacket 3 is itself provided with a series of spray holes 5 arranged around the lower part of the jacket, either formed in or mounted on the walls of the mould 1 so that water in the jacket flows out of the spray holes 5 to impinge on and cool the dummy when it is in its initial starting position, as shown in FIG. 1, and subsequently to impinge on and continually cool the cast billet as it emerges from the mould 1 when the dummy is lowered.

The upper surface of the dummy 2 can be flat or provided with a recess, leaving a narrow land 7 around the periphery of the dummy. Such recess, however, is designed to suit the metal feed arrangements and does not concern this invention As particularly shown in FIG. 2, in carrying out one embodiment of the invention, before the commencement of a casting operation, a strip 8 of heat resistent material preferably woven fiber glass cloth, is laid round the inside of the mould along the corners formed between the side walls of the mould and the dummy 2, the strip of cloth 8 lying at least over the land 7 on the dummy 2, and extending a short distance up the inside of the walls of the mould 1. The material strip 8 is pressed into the corners so that a sharp corner is presented to the molten metal.

The fiber glass cloth strip 8 initially contributes to the seal between the dummy 2 and the mould 1 when molten metal is first poured into the mould, and as the molten metal solidifies in the bottom of the mould on top of the dummy 2, the fiber glass cloth strip 8 becomes attached to the surface of the solidified billet.

When the dummy 2 is lowered and the solidified billet progressively emerges from the mould l, the fiber glass cloth strip 8 retains and prevents run-out of molten metal from any part of the surface of the solidified billet beneath the strip as it contracts away from the mould l and locally remelts as discussed in the preamble of this specification.

When the casting of a billet is complete, and the whole billet is cooled and solidified, it is possible to remove the fiber glass strip 8 leaving the cast billet substantially free from the run-outs thus elliminating the time and labor cost which would have been incurred in their removal.

It is to be understood that the primary requirement of the heat resistant material for the strip 8 is that it will withstand the temperature of the molten metal to be cast, and other materials than fiber glass may be used, although fiber glass is the preferred material for use in the casting of aluminum and its alloys.

While in the embodiment described with reference to FIG. 2, the fiber glass cloth strip 8 is shown as being arranged around all of the four sides of the rectangular mould 1. It is to be understood that in many instances it is not essential that the cloth strip is placed around each side, and it may in some cases be sufficient to only provide the cloth strip at the ends along the shorter sides of the mould l where the shrinkage away from the mould walls is usually most acute.

In a development of the invention, the use of the strip 8 may be extended to alleviate blebbing on the sides of the cast billet. As discussed in the preamble of this Specification, blebbing results from the surface of the cast billet remelting during the cooling process and small quantities of liquid metal escaping to form blebs or protruberances on the side of the cast billet.

If the fiber glass cloth strip 8 laid around the bottom of the mould before the commencement of casting is continued as a sheet up the side of the mould l, and a roll of such cloth as indicated at 10 in FIG. 3 is provided, so that as the dummy 1 is lowered the glass cloth can move down the side of the mould 1 with the progress of the casting operation, being continually supplied from the roll 10; it can be seen that the whole of a side of the cast billet can be protected by a sheet of glass cloth material. This glass cloth material again adheres to the side of the cast billet, and retains and thus prevents the locally remelting metal in the surface of the cast billet beneath the material from forming belbs.

It has been found, that the use of the fiber glass material strip 8 around the bottom of the mould before commencement of casting has also served to reduce the curvature of the cast billet caused by shrinkage away from the dummy 2 during cooling as discussed in the preamble of this specification.

The effect of the fiber glass material is to restrict the cooling effect of the water spray system on the billet issuing from the mould to such a degree that the differential shrinkage between the metal first solidified on the dummy and that immediately following is significantly reduced, with a corresponding reduction in the degree of upward bowing of the edges of the bottom surface of the billet.

FIG. 4A shows a side view of the lower end of a typical cast billet with a curvature height indicated at X," X being as much as three inches on a billet which may be some 62 inches wide, and FIG. 4B shows a similar view of billet cast in similar alloy with the use of the glass cloth strip 8 and for which the height of the curvature has been reduced to substantially X/2. FIG. 4c illustrates a consequence of excessive curvature in that a high stress region is created in the center of the billet which can cause a stress crack during cooling as indicated at 20 in that FIG, particularly in the casting of alloys of aluminum having significant quantities of magnesium and/or copper in their analysis. The creation of such stress cracks can be substantially avoided by the reduction in curvature which arises with the use of the glass cloth strip 8.

Further both the formation of run-outs at the lower ends of the cast billet, and the formation of blebs on the surface of the cast billet, particularly run-outs and blebs at one of the end faces of the cast billet, can result in the jamming of the billet in the mould 1 on one side thereof with the result that the cast billet only descends during casting on one side. Such jamming, or stick up results in a grossly distorted billet; and if, as frequently happens, the jammed end of the billet becomes free for some reason and suddenly drops down so that the cast billet again lies squarely on the dummy, it can result in a sudden flow of metal from the mold 1 over the top of the then free end of the billet. Such flow of molten metal is not only wasteful but can be extremely dangerous to personnel operating the process.

It has been found that the elimination or substantial reduction of run-outs and blebbing by the use of the glass cloth strip has reduced the incidence of stick up or jamming of the billet in the mould 1 to negligable proportions.

Thus it can be seen that the provision of the heat resistant material strip 8 around the bottom of the mould before the commencement of casting, results in an improved casting performance and economy.

What I Claim is:

l. A method for the semi-continuous casting of a metal billet in a mould having a vertical wall structure and a dummy which is initially disposed within the lower part of that wall structure, said dummy being lowered progressively from the wall structure as metal in the mould solidifies and casting proceeds, comprising laying, before metal is poured into the mould, a strip of heat resistant and thermally insulating sheet material around at least part of the peripheral corner formed between the dummy and the inside of said wall structure, said strip extending onto the upper surface of the dummy and turned upward to extend at least a short distance up the wall structure above the upper surface of the dummy, and said strip being attached to the billet as the molten metal solidifies in the bottom of the mold on top of the dummy so that it confines the side of the lower end of the cast billet as it emerges from the mould.

2. A method as claimed in claim 1 wherein said mould is of generally rectangular cross-section, and said strip material is laid along at least one side of the mould.

3 A method as claimed in claim 1 wherein said heat resistant sheet material is fiber glass cloth material.

4. A method as claimed in claim 3, wherein said cloth material is a woven fabric.

5. A method as claimed in claim 1 wherein said heat resistant and thermally insulating sheet material is laid along at least one Side of said rectangular cross-section, extends up the full height of the respective side of said wall structure in a continuous sheet to lie between metal cast in the mould and that side of the wall structure, means being provided to feed said sheet continuously to and down that side as casting progresses.

6. A method as claimed in claim 1 wherein said wall structure is water cooled.

7. A method as claimed in claim 1 wherein said dummy and the cast billet emerging from the mould are cooled by means of water sprays. 

1. A method for the semi-continuous casting of a metal billet in a mould having a vertical wall structure and a dummy which is initially disposed within the lower part of that wall structure, said dummy being lowered progressively from the wall structure as metal in the mould solidifies and casting proceeds, comprising laying, before metal is poured into the mould, a strip of heat resistant and thermally insulating sheet material around at least part of the peripheral corner formed between the dummy and the inside of said wall structure, said strip extending onto the upper surface of the dummy and turned upward to extend at least a short distance up the wall structure above the upper surface of the dummy, and said strip being attached to the billet as the molten metal solidifies in the bottom of the mold on top of the dummy so that it confines the side of the lower end of the cast billet as it emerges from the mould.
 2. A method as claimed in claim 1 wherein said mould is of generally rectangular cross-section, and said strip material is laid along at least one side of the mould.
 3. A method as claimed in claim 1 wherein said heat resistant sheet material is fiber glass cloth material.
 4. A method as claimed in claim 3, wherein said cloth material is a woven fabric.
 5. A method as claimed in claim 1 wherein saId heat resistant and thermally insulating sheet material is laid along at least one Side of said rectangular cross-section, extends up the full height of the respective side of said wall structure in a continuous sheet to lie between metal cast in the mould and that side of the wall structure, means being provided to feed said sheet continuously to and down that side as casting progresses.
 6. A method as claimed in claim 1 wherein said wall structure is water cooled.
 7. A method as claimed in claim 1 wherein said dummy and the cast billet emerging from the mould are cooled by means of water sprays. 